1. Field of the Invention
The present invention relates to an apparatus for suppressing noises in a video signal.
2. Description of Background Information
Recently, there has been proposed a wide band video disk (simply referred to as SLD hereinafter) on which is recorded a recording signal from which FM audio carrier signals (of 2.3 MHz and 2.8 MHz) of ordinary video disks (simply referred to as LDs hereinafter) are removed in order to improve the horizontal resolution of the video disk, and a high frequency part of the color composite video signal (simply referred to as the video signal) is expanded, upon recording, into the frequency band remaining unused after the removal of the audio carrier signals.
With this method, the signal bandwidth of the recording video signal can be expanded from conventional 4.2 MHz to the extent of 6 MHz.
In the case of the SLD, if there is any factor generating distortions in the optical reading system such as the formation of pits, or in the signal transmission path such as in the head amplifier, the demodulated video signal which is retrieved by the playing apparatus will be degraded by a beat disturbance. Moreover, there is a tendency for the beat disturbance to become more noticeable with color pictures in which the signal spectrum is more concentrated as compared with monochromatic pictures.
This point will be explained with reference to the accompanying drawings.
FIG. 4 shows a signal spectrum of a radio frequency (simply referred to as RF) signal (FM modulation signal) read from an SLD by means of a pickup of a conventional arrangement, under a condition that a beat disturbance is generated in a color picture. As illustrated, upper and lower sideband components (.omega..sub.c .+-..omega.sc) of a color subcarrier signal are present at frequencies spaced from the frequency of a main carrier .omega..sub.c by .+-..omega..omega..sub.sc. Moreover, beat components due to the distortion are generated as frequency components .omega..sub.sc and (2.omega..sub.c-.omega. .sub.sc).
FIG. 5 shows a frequency relationship between the color subcarrier signal .omega..sub.sc and the beat component (.omega..sub.c -.omega..sub.sc) when the RF signal shown in FIG. 4 is demodulated by an FM demodulation process. The beat component is generated as a component (.omega..sub.c -.omega..sub.sc) above the color subcarrier signal .omega..sub.sc. Since the frequency of the main carrier generally ranges from 8.1 MHz to 9.3 MHz, the frequency of the beat component (.omega..sub.c l -.sub.sc) ranges from 4.52 MHz to 5.72 MHz when the frequency of the subcarrier signal is 3.58 MHz.
With conventional LDs, this beat component does not cause any problem because its frequency ranges outside the bandwidth (below 4.2 MHz) of the video signal. However, in the case of the SLD, the bandwidth of the video signal is as broad as 6 MHz, and the beat component will appear in the video signal bandwidth. Therefore, a problem arises such that a bar-pattern noise appears in the picture.